The most widely used supercapacitors have electrodes made either of active carbon or else of a metal oxide deposited on a collector.
The metal oxides generally used are oxides of ruthenium or of iridium. These oxides are obtained by thermally decomposing chlorides under oxidizing conditions at temperatures of about 350.degree. C. to 400.degree. C., as described in South African patent No. 662 667. The methods usually used for preparing them give rise to a compound that is not very porous. Practical capacitance densities as measured on such electrodes are less than 100 Farads per gram of active mass.
Practical capacitance densities of about 150 Farads per gram of active mass have been obtained using electrodes made of active carbon. However work on such materials leaves no room for significant progress.